Radiation melting furnace



Jpne 29, 1954 N. R. WAHLBERG- RADIATION MELTING FURNACE Filed Oct. 26, 1951 Patented June 29, 1954 RADIATION MELTING FURNACE Nils R. Wahlberg, Iggesund, Sweden, assignor to Iggesunds Bruks Aktiebolaget, Iggesund, Sweden, a company of Sweden Application October 26, 1951, Serial No. 253,250

9 Claims.

The radiation melting furnaces in practical use up to the present time are of two different types, partly electric arc furnaces and partly resistance heated radiation furnaces in which energy is supplied by resistance heating of a radiation unit.

If energy is supplied by radiation in the case of electric arcfurnaces this leads to the inconvenience that the temperature of the source of radiation (the electric arc) cannot be regulated. In a furnace filled with gas, energy is transferred also by convection, and the temperature of the roof of the furnace above the source of radiation may rise to a level where risk of the roof melting is incurred. To an extent the risk of melting of the roof in electric arc furnaces due to high temperature radiation and simul taneous convection can be neutralized by arranging the electric arcs vertically. By this means the electrodes between which the electric arc is formed will shade the furnace roof to some degree. On the other hand such an arrangement complicates the regulation and control of the electrodes. In such cases automatic control will be insufficient, as there is a risk of the charge getting into contact with the electrodes and producing electric arcs at unsuitable spots, which may lead to the electrodes burning off. In the same way the electrodes may be broken if larger pieces of the charge while melting drop upon them. Therefore continuous personal supervision is necessary with such furnaces.

' The efforts to avoid the inconveniences thus connected with electric arc furnaces, at least for certain purposes, have lead to the construction of the reasons for this is probably that the junker furnace is filled with gas or air, which makes it unavoidable that heat is transmitted to the furnace roof above the resistance or radiation units by convection. As the temperature of the radiation unit is about 2,000 C. or more, the transmission of heat through simultaneous convection and radiation will take place at such a high rate, that there is danger of melting the furnace roof.

Starting from the above considerations a new resistance radiation furnace has now been constructed in which the danger of melting the furnace roof is eliminated or at least considerably lessened. According to this invention the furnace consists of a furnace space with resistance heated radiation units arranged within a part of the furnace space opening towards another adjoining part of the same furnace space intended for receiving the charged material, at least the roof above the radiation units slanting in a way which partly reflects the heat rays reaching it from the radiation units towards the part of the furnace space which contains the charge and partly leads the hot gases rising towards this where E=energy supplied 7c=a constant F=radiation surface T=absolute temperature of the radiation surface that T will be kept below the temperature at which the material of the furnace roof will melt.

A further guarantee against excessive temperature of the furnace roof above the radiation units is provided by slanting the roof sothat the convection currents are led towards the charge introduced into the furnace. Thus the convection heat will be conducted to the charge and contribute to the melting thereof, at the same time resulting in a circulation of the furnace atmosphere preventing overheating of the roof. By slanting the other walls of the furnace appropriately the secondary radiation therefrom or the reflection of the primary radiation may be directed towards the charge, which further increases the efficiency of the furnace.

The furnace according to this invention should preferably be so constructed as to be tight and function with a neutral or reducing atmosphere, preferably carbon monoxide, e. g. from a producer gas unit, partly in order to protect the radiation units consisting of carbon or graphite and partly to prevent the formation of iron 3 oxides in the slags and slag damage upon the furnace lining.

In the following a more detailed description of the invention will be given with reference to the accompanying diagrammatic drawing, which shows a suitable embodiment. Fig. 1 shows the furnace from above and partly in section, Fig. 2 is a longitudinal section of the same furnace.

In the drawing 1 is the body proper of the furnace, which encloses the furnace space 2. A series of heating resistance elements 3, in the embodiment illustrated there being six, extend through the space 2, which heating elements due to the form of the furnace space have different lengths and, therefore, are arranged in pairs coupled in series in such a way that the total resistance of each pair is approximately equal. By this method of arranging the radiation units or heating elements it is possible to obtain a radiation surface of such size that sufiicient energy for melting can be supplied at a temperature which involves no risk of melting the furnace I roof.

the heat rays that reach them to reflect and secondary radiation to be directed towards the charge, thus greatly increasing the efficiency of the furnace. By suitably designing the walls of the furnace it will theoretically be possible to keep the temperature of the walls and roof below the melting temperature of the charge.

The furnace is provided with an opening is for charging and a tappinghole l and furthermore on the front side a door 8 for inspection and cleaning, which is equipped with two observation openings 9, iii, the one 9 directed towards the melt and the tapping-hole and the other Hi towards the heating elements. All these openings can be closed so that the furnace can operate with a suitable protection gas, e. g. producer gas. The tapping-hole 1 consists of a substantially cylindrical. opening l l in which a refractory cylindrical brick H2 is inserted. The brick has a central opening is in the form of a double cone tapering from both ends inwardly. The lower cone I4 is lined with a hollow graphite body I5 having an annular inward enlargement I'B at the top. The lower mouth of the central opening I3 is closed by a detachable lid H pressed against the outer furnace wall by means of a wedge 18 mounted therebelow on sleeves l9 slidable on guides secured to the furnace wall.

The furnace can. preferably be tilted or at least tipped in three different positions, namely one for charging, when rear wall is swung down so as to receive the main jolts when the charge is introduced, one for melting, which corresponds to the one shown on Fig. 2 and one for tapping, where the front end is swung down so that the melt now out through the tapping-hole '5. When the furnace tilted back to middle position after tapping it very often happens that some iron and slag left in the tapping-hole. To keep this from solidifying one of the heating elements should be arranged in such a way that its radiation is directed towards the tapping-hole, as is the case with the leftmost heating element on Fig. If one of the heating elements is arranged in such a way and there is a superatmospheric pressure in the furnace, it is to a great extent possible to prevent iron and slag from remaining in the tapping-hole when the tapping is over.

What is claimed is:

1. A melting furnace comprising a roof, a bottom, sidewalls, and endwalls confining a furnace chamber, a charging opening in said roof adjacent one of said endwalls, the space below said charging opening along said one endwall forming a charge zone of said chamber, the remainder of said chamber forming a radiation zone, a plurality of electric resistance elements arranged substantially horizontally and transversely in said radiation zone, said roof being inclined upwardly toward said charge zone so as to promote circulation of the atmosphere in said chamber along said roof toward said charge zone and to radiate towards said charge zone.

2. A melting furnace as claimed in claim 1 in which. sidewalls diverge in the direction towards said charge zone so as to improve the radiation from said sidewalls towards said charge zone.

3. A melting furnace as claimed is claim 2 in which said elements are different in length and are arranged in pairs electrically coupled in series so as to make the total length of the elements of each pair substantially equal.

4. A melting furnace as claimed is claim 1 having a discharge opening in said bottom remote from said charge zone, and a lid for closing said opening fromoutside.

5. A melting furnace as claimed in claim 4 in which said bottom of the furnace is inclined downwardly towards said charge zone to form a melt wall zone below the mouth of said discharge opening.

6. A melting furnace as claimed in claim 5 comprising means for tilting the furnace about a horizontal axis transversely thereof.

'7. Amelting furnace as claimed in claim 5 in which at least one of said heating elements is positioned above said discharge opening so that radiation from said element will penetrate into said discharge opening.

8. A melting furnace as claimed in claim 1 in which the total heating surface of said elements is at least so great relative to the inside surface of said furnace exposed to the radiation from said elements that the energy required for keeping the molten charge can be supplied through said elements at a temperature of said elements which is so low that the temperature of the roof of the furnace will be below that temperature at which the material of the roof will melt.

9. A melting furnace comprising a roof, a bottom, sidewalls, and endwalls confining a furnace chamber, a charging opening in said roof adjacent one of said endwalls, the space below said charging opening along said one endwall forming a charge zone of said chamber, the remainder of said chamber forming a radiation zone, a plurality of electric resistance elements arranged substantially horizontally and transversely in said radiation zone, said radiation zone opening towards said charge zone in such manner that radiation from said elements will reach said charge zone after one reflection against the roof of said radiation zone, the total heating surface of said elements being at least so great relative to the inside surface of said furnace exposed to the radiation from said elements that the energy required for keeping the charge molten can be supplied through said elements at a temperature of said elements which is so low that the temperature of the roof of the furnace will be below that tem- 5 perature at which the material of the roof will melt.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 761,920 Schneider June 7, 1904 762,270 Benjamin June 14, 1904 1,088,496 Wedge Feb. 24, 191 10 1,167,176 Highfleld Jan. 4, 1916 1,367,364 Erlchsen Feb. 1, 1921 1,547,000 Ruckstahl July 21, 1925 Number 6 Name Date Hitner Dec. 14, 1926 Bunce et a1 June 26, 1928 Benner et a1 Oct. 20, 1931 Seliger et a1 May 23, 1939 Delpech Sept. 10, 1940 Poland June 7, 1949 OTHER REFERENCES W. Trinks, Industrial Furnaces, vol. I, published in 1934 by John Wiley 8: Sons, Inc., N. Y. (Copy in Div. 3.) 

